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A web-site by Rob Speare


Rebuilt Merchant Navy Class Pacific - 'Bibby Line'.

words and drawings by Ian Tiplady.

As a young boy I can just remember these locos going past my grandmother's house at a distance across the sewerage farms at Berrylands, viewed from the Kingston road.  Occasionally I got nearer when my dad took me out to see the trains.  We even got a ride on the footplate of 34013 Okehampton, when I was about 7-8 years old.

Just as I was becoming old enough to go watching the trains on my own, steam hauled trains came to an end.  What was worse, I did not know it was happening until it was reported on the TV news, showing the last one leaving Waterloo;
a bitter blow for a 12 year old, looking forward to driving one when I grew up.

Later in life after getting into model railways and a few visits to some local miniature railways and exhibitions, I got interested in building a larger model.  Copies of M.E. magazine were collected regularly so I could start learning techniques until a workshop was available.  After obtaining a small Zyto 3 3/8" lathe and a set of 3½" gauge 'Molly' castings I set about building it.
I now found that the metalwork classes from school days did not cover all the processes I needed, and I had a steep learning curve with the machining of the wheel castings.

When Keith Wilson's 'Ariel' design for a Merchant Navy class was introduced, I was smitten - this was the type of loco I wanted to build.  'Molly' went onto a shelf - it's still there - and my attention moved to the new project.  I collected the M.E. write-ups and obtained some castings to build the chassis.

I started with the bogie and followed drawings and instructions.  It went together well and looked the part, so it was painted and put away so I could start on the main frames.  About this time I was thinking about a name, and started to collect information on the Merchant Navy class.  My model railway days had turned me into quite a purist when it came to prototype correctness, and I had a number of books etc, but on the GWR - so my knowledge of M.N. locos was very limited.

Having decided on 'Bibby Line' right after it was rebuilt (c.1956, 6000 gal tender, cast bissel truck, no aws battery etc.) as my loco to copy, I started to collate as many pictures and general info as I could.  With this new knowledge I started to see the detail differences that had been pointed out between BofB and M.N. locomotive motion brackets, and set about redrawing Keith's drawings where needed.  I apologise here for my sketches, I am no draughtsman, (an "O" level in technical drawing a long time ago), and most of the drawings are pencil and paper, done as needed and then amended/redrawn/redesigned as I built the items.  My drawings are only a supplement to Keith's so you will need access to an original set of drawings, or the write-ups in M.E. magazine that started in 1983.

By this time I had made the main frames and found out that arc welding was not among the skills I possessed, but I managed to weld up the frame spacers etc. and then with the use of a MIG welder the inside motion bracket was made.  If you have not worked out what the flat plates on the top of this bracket are for, they are the mountings for the boiler.  There are two brackets fixed onto the boiler, which are then bolted to these plates, the expansion being allowed on the rear support/brake bracket.

I found the MIG more controllable, but they were not very pretty welds.  However, as they were hidden inside the frames and did not show, they were cleaned up using an angle grinder.  In the mean time other details emerged, and after I had built the bissel truck I went back to the bogie.

Bogie truck.   After a trip to the Watercress line to see 'British India line' (35018), I redesigned the spring control bosses, they are more rounded and the spring control end cap is level, so this was rectified as my drawing No.1, repainted and put back into store. 
The only thing I could not change easily was the use of 1/8" rivets; if I was building new I would have used smaller 3/32" ones because the bigger ones heads need thinning down behind the wheels.

Bissel truck   Not having the confidence to make a good job of the outside brackets, I put these aside and turned my attention to the bissel truck.  The drawings for this piece are a bit of a hotchpotch.  Keith admits this and has made a compromise of cast and welded types.  From his drawing either type can be made, if you decide on welded type just replace the cast sides with 1/8" sheet and fabricate the spring pockets/horn cheeks (use a good photo).

I took this path as I already had castings, using a good picture of the cast truck to redesign the 'welded' frame to look like a cast one (see bissel truck drawing), completed using MIG welding.  I cut out and bent to shape the frame parts, then welded these edge to edge to the mounting plates, the "I" beams were then tack welded in place and silver braised.  I bent the gun metal casting just in front of wheels as per the prototype, see bissel truck drawing.  The other modification was to the bearing pad holders; I machined a ring out of the same bar and silver braised three small lugs on, just like the real ones.

Smoke box and saddle   I was still shying away from motion brackets, so next I attempted the saddle; this was made as Keith's drawings and put aside.  Later when trying to marry it to the inside cylinder I thought there must be an easier way without using a bucket of filler.  The difficult bit is machining the curve to match on the inside cylinder casting.  So I thought why not get rid of the curved bit, so I milled them off to replace them with a bolt on fabrication and then joined this to the front piece.  But still the thought of making it airtight lingered, so a study of the prototype showed the way - a box with a lid inside the smoke box.  So I redesigned the whole lot with one fabrication as per my saddle drawing.  It appears to work quite well, and is a lot easier to seal.  So far 2 small points have come to light:  1st) - roll the smoke box and match the curve on saddle before welding/braising it all up;  2nd) - the dart bars will need adjusting to fit in the new space available.

This seems to be a good time to mention the modifications I did to the smoke box door and hole.  Whilst studying photos of the saddle I noticed a small flat section to the top and bottom of the door, thus to me, making the door an oval rather than an ellipse.  This means it can be machined with a fly cutter.  So I made a new pattern and got a new slightly larger door casting made, which also allowed me to put a rim around the door and a small lip around the hole;  see the smoke box door drawing.

Another omission on Keith's drawings is of the inside cylinder valve guide.  I have used Doug Hewson's casting for his B.R. standard type 4, and made some bronze slides to fit around the valve crosshead I had already made to Keith's drawing.  However I will use the crosshead upside down with the flat guide plate at the bottom, so closer to the bracket, and allowing the slides to be a lot lower (they looked rather awkward before).
Unfortunately after making the piston crosshead slide bars I found that the two units overlapped, and I had to take a file to the valve guide, see photo.  When I get a chance I will remake both guides.

Outside brackets   Now back to the parts I had been avoiding.  The outside brackets as described by Keith were all of W.C./BoB design.  So using the photos and sketches I had of 'British India Line' (35018) I have redrawn all the parts that are needed.  Some explanation may be needed on each of them; firstly the reverse bracket;  the only part used was the actual reversing mechanism, from the top plate down it has new plate work and shape, so the back plate (1), sides (4 & 5), bottom (13), lugs and top plate holes have been changed, (see reverser bracket drawing).  After cutting out all the pieces and bending the side plates, to assemble I used a method I had read about in M.E. magazine.  This involved a small unobtrusive or to-be-hidden tack weld to hold the parts together, and then when satisfied the fabrication is braised up in one go and any tack welds can be ground off.  Of course if an edge can be fully welded together, like top and sides, it will be a bit stronger.

After this success I tackled the motion bracket, again redesigning the relative parts (see motion bracket drawing).  These were the base plate (1), side plates (3 & 4), front and rear (5 & 6), bottom (7), gusset plate (8), flange plates (10) and lugs (11).  Keith suggests a jig to build these on; it is well worth the small amount of effort involved.  In the redesign of this item it lowers the brake lever lug 3/16".  Oh dear!  So hours of pouring over drawings and photos, in my growing collection of books and pictures, showed that all of these pivots are the same relative height, and if this is so, the reverse bracket lugs are too high.

So it was back to the drawing board for the reverse bracket; the base and side plates were remodelled and the unit dismantled and rebuilt.  I thought about but did not alter the brake lever length to account for this, (losing the will to live), and moved on.  The motion bracket has a triangular fixture protruding from the front, this matches a similar fixture on the slide bar bracket, and together they support two lengths of angle with the lubricators mounted on them.  The expansion link bearings are not shown on Keith's drawings, but from 35018 it looks like a cup and saucer on edge with a cover over the end (see motion bracket drawing).

Slide bar brackets   Not much redesign on this, I wish; - because there is no angle on top plan view and the bearing for swing link is halfway through platform, nearly all parts needed altering in some way.  The main parts that are ok are the base (1) and bottom (8) and platform support (14).  The raising of swing link bearing by 5/32" also means lengthening of the link itself by the same amount, not made this bit yet, see slide bar drawing for details.  If you want to build 35018 as newly rebuilt, the lubricators were mounted on top of slide bar bracket hence the cut out in part (9) for the rocker bar assembly.  I don't know when they were moved but when 'Bibby Line' appeared, the second one to be rebuilt, it had lubricators in between the brackets and the rocker assembly affixed underneath angle supports.  For any other loco, ignore the 3 holes and the cut out.

Other brackets   Along the frames there are several platform support brackets, nothing too difficult if you have completed the others (see platform bracket drawing).  One bracket that is detailed, unfortunately needs modifying; the one on the opposite side of reverse bracket, it is also modelled on BofB type.  I have redrawn it to M.N. design and also lowered the brake pivot to match all the others (see brake details 1).  Also on this drawing you will see a new design of rear brake/boiler support.  This replaces the BofB type and is detailed on several drawings.

Cab supports  
Another part that Keith was unsure about was the front cab support, and I have redrawn it from my own observations.  The main change is that it is not attached to the sides of frames but sits on top of the bissel truck bearing beam and drag box (see various drawings for details).  I have added 4 lengths of ¼" angle across the tops to mount the cab sides and floor to make this one unit.

I have not shown the steam generator platform, this was fixed between the cab supports.  It was bent up at the rear to meet the rear support, and at the front attached (both braised) to the mounting plate on top of the bissel truck support beam.  On the opposite side there is a cross bar to give somewhere to affix the injectors about level with the angle on the sides.  See a photo of rear drag beam and you will see 3 bolts grouped together.  I have not finished this area yet; there are 4 triangular brackets for fall plate and the side plating.  On the drag beam I have added a flat plate, 1/8" thick thinned down each end, as rubbing plate for tender snubber (see cab layout drawing).

Brake gear   Now I come to the brake gear.  Over the last year or so I have found someone building a Bulleid West Country class, who has access to laser cutters and CAM.  So I have had a number of parts made, such as pull rods, upper levers and compensation link 1 to start with, the rest I did by hand.  There are a number of mistakes and omissions on Keith's drawings.  The main mistake is the front compensation beam 1, the profile is correct, but there are 4, 2 each side, held apart by a spacer.  The front brake lever, which is sandwiched between the compensation beams, although the profile is right the end view is not (see brake details 1).  There are no offsets in the pull bars so I spaced mine at 5/8", 1/32" wider.  There are 3 cross rods shown on Keith's plans but only 2 are used.  The front one is in the right place, but the middle one goes through the top hole in the compensation link 3 and the bottom end of brake hanger lever (so this one needs 3/16" ends).  The rear cross rod is not used.

The main omission is the brake adjuster in the pull rods between the now empty cross rod hole and centre hole of link 3 (see brake details 1) shorten pull rod to this hole.  I have used flat sheet for all the brake levers and made separate spacers / bosses of various sizes; undecided as yet whether to solder them up; I'll see how sloppy it is when it is fitted.  I have soldered the spacers between compensation link 1 and top brake hanger levers.

After assembly of all the brake components a few changes were needed to my drawings of the main pull bar, (drawing updated).  I had already made the cross beam, so had used -

3/16" pins with two pull levers, 3/8" at one end tapering to 1/8".  I then found they fouled the front spring bracket, so I have milled away the outside face of each to give clearance.  It looks in the photo below that it was thinner (about ¼").

That is my story of the changes I have made so far, I hope it helps if you are building Ariel.  I have a few items on the back burner, mainly the tender, but also cab and boiler.  The cab parts and tender frames have been laser cut, and I have an order for 3 sets of valve gear rods (CNC), and am awaiting some castings from Doug Hewson.  I recommend looking at his castings for steam drain cocks and snifter valve, along with many other B.R. fittings.

At present I am still completing a Winson/Modelworks kit of GWR 4575 class, which I thought would be a fairly quick build, but it has been a case of "I think there is a better way of doing that", and this has side tracked me a great deal and it is occupying my building stand.  When I get that free, I can start to assemble all the parts laying under benches or on shelves - if I can find them.